I agree with peteb, but I'd say not at all. You cant weld copper for a start- solder/braze but not weld, Aluminium you can weld, but not to copper, aluminium is a very awkward material when it comes to joining, which is why aluminium welding is expensive to get done. as peteb said, the "way" they are joined is very important as far as heat transfer goes.
Next time you wave - use all your fingers